British Airways cabin crew will take their 20th day of strike action today, with no sign of a breakthrough in their bitter dispute with the airline. Members of Unite will remain on strike until Wednesday, but the union is threatening to hold a fresh ballot if the deadlocked row is not resolved soon, which could disrupt flights in the busy summer months. The cost of the industrial action to BA will be well over £150m by the time the current strikes end on Wednesday. The impact of the dispute was revealed this week when the airline announced a 14.2% dip in passenger numbers last month.

A BA spokesman said: "The numbers of crew reporting for work at Heathrow has been higher than we expected and as a result we have been able to operate additional flights to Los Angeles, Washington, Mexico City and Phoenix."BA is aiming to operate around 80% of long-haul flights from Heathrow despite the strikes, up from 70% and 60% in the past two strike periods, and 60% of short-haul flights, up from 55% and 50%.

Talks between Unite's joint leader Tony Woodley and BA's chief executive Willie Walsh under the auspices of the conciliation service Acas ended without agreement last week, with little sign of any progress.

An agreement in principle has been struck over cost-cutting, the original cause of the dispute, but the removal of travel concessions from strikers is now blocking a deal.

Unite has urged BA to fully restore the travel concessions, arguing it would not cost the airline any money.

Derek Simpson, Unite's joint general secretary, said today: "I have made it clear that as joint general secretary I am available any time day or night to meet with BA and Willie Walsh to attempt to resolve this dispute.

"BA is the real obstacle. We have made it absolutely clear that if BA re-instates our members' travel concessions we would suspend the strike action. This would cost the company nothing. Instead the company is willing to see its passengers' travel plans disrupted while the airline loses millions."

An Acas spokesman said: "Acas and the TUC have continued to maintain contact with both BA and Unite since talks were adjourned.

"It is expected that a date will be agreed shortly for talks to resume."